Scenario Runner

[temyers]

Creates Cucumber runners based on Scenarios, rather than Features to enable greater parallelisation.

• Have created a new property to choose the method, for backward compatability.
• The original feature based generator has been deprecated, with the intention of removal in version 3.

Rerun functionality is outside the scope of this PR. A separate PR shall be created.

Changes from PR #53

• Gherkin added as a Maven dependency, rather than source inclusion
• Mechanism for filtering scenarios by matching tags has been rafactored into a separate class. This enables the same mechanism to be used by both file generation schemes, with the added benefit that full tag filtering is now possible (excluded tags are processed)
• Feature based generator is maintained for backward compatability